Plant Disease and Diagnosis€¦ · 24/02/2020 · Nutritional Deficiencies •Nitrogen •Highly...

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Plant Disease and Diagnosis

Dr. Tamla Blunt

Plant Pathologist

Colorado State University

Why Do We Need to Know Plant Pathology?• A lot of the questions at the Help Desk are about

plant problems• Plant Pathology give you a background in types of

plant problems• Terminology/definitions/descriptions are important

in Plant Pathology (kind of like a foreign language)• We use terms like ‘generally’, ‘usually’, ‘consistent

with’, ‘sometimes’, ‘it depends’• A background in PP can help you with the

diagnostic process; determine what questions to ask your clients

Plant Problem Diagnosis

Diagnosis –process used for the identification of problems; consider it ‘CSI’

for plants

Tools:• Plant sciences, especially plant pathology and

entomology• Art of investigation and detective work

Some Other Tools• Items that are handy to

have in a sample collection/plant diagnostic toolbox:• Hand lens/ magnifying

glass/binoculars;• Pocket knife;• Soil probe;• Shovel;• Small notebook

w/pencil;• Plastic baggies;• Small saw/hand pruners

What is a Plant Disease?Abnormal growth/ dysfunction of a plant

Environment Causal Agent

Host

Plant Disease Pyramid/Triangle

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Plant Problem Diagnosis Steps• Know the normal appearance of the plant

• Symptoms and Signs

• Abiotic vs. Biotic• Review environmental conditions

• How do symptoms/signs progress?

• Review cultural practices

• Observe patterns

• Ask questions

• Consult literature/control measures/final diagnosis

Identify The Plant

•Why?• Typical “MO”• Known “enemies”• Is this normal?• Is it normal this time of

year?

Identify The PlantKnow Normal Appearance

of Plant• Plant identification.

• Scientific vs. common names

• Variety or cultivar

• Recognize healthy plant appearance.

• What’s normal?

Is This Normal For These Plants?



• Abiotic vs. biotic• Review environmental conditions




• Ask questions


SymptomsSymptom: A plant’s reaction

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Chlorosis: Loss of Green ColorMosaic: Varying Patterns of Light and Dark Plant Tissue

Necrosis: Dead Plant TissueBlight: Sudden Death

Wilting: Limp, Droopy Canker: Sunken, Discolored Areas

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Stunting: Lack of Plant Growth Galls: Localized Swellings

Distortion: Mal/De-formed Plant Tissue

Where are the Symptoms?

• Leaves

Phyton 27 damage to poinsettia


• Stems (BUT leaves or other parts above stem may also show symptoms)


• Roots (BUT plant parts above may show symptoms)

Root Rot

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Flowers

Fruit







• Ask questions


SignsSigns: Presence of the actual organism causing the problem

Ooze: Slime-like droplets(Bacteria)

Usu.edu

Fruiting Structures (Fungi)

Cleistothecia Acervuli with setae (bristles)

Perithecia

Fruiting Structures Embedded in Plant Tissue

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Hyphae: Thread-like Vegetative Growth of Fungi; Mycelium is a Mass of Hyphae

Spore Structures: Hold Masses of Fungal Spores

Mildew: Whitish Growth Produced by Specific Fungi

Mushrooms/Conks: Fleshy or Firm Reproductive Structures

Symptom vs. SignSymptom = effect Sign = cause

Symptoms vs. Signs

Example: Lilac

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Symptoms vs. Signs

Recently killed tissue (halo)

Fruiting Structures(underside)

Group Activity

But first, using a hand lens!Symptoms vs. Signs Activity 1

Symptoms vs. Signs Activity 2

This sample

These samples

+







• Ask questions


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Causal Agents of Plant Disease

• Biotic = living causes such as microorganisms

• Abiotic = non-living causes such as the environment

Abiotic Causes of Disorders:

• Too low/too high temperatures

• Lack of/excess soil moisture

• Lack of or excess light

• Nutrient deficiencies

• Soil type/pH

• Pesticide toxicity

Weather- Related Problems:

• Yearly dry fall/winter period

• Drought

• Late spring freezes

• Prolonged cool wet weather

• Early fall snow

• Sudden fall freeze

• Hail

• Flooding

Temperature

• High Temperature Effects• Plants are generally

injured faster and to a greater extent when temps become higher than the maximum for growth

• Sunscald• Cankers • Leaf scorch

Sunscald aka SW Disease of Trees• Intense radiation by

sunlight on south or southwest side of thin-barked trees

• De-acclimates bark• Predisposes to temperature

damage• Freezing/thawing

• Sunscald predisposes trees to canker pathogens

• Protect bark• White paint (water-based)

• Boards

• Paper wraps (be sure to remove in spring)

Photos by Bill Jacobi

Honeylocust & Ash tree

with sunscald damage

Temperature• Low Temperature Effects

• Does more damage to plants than high temps

• Kills buds, flowers, leaves and twigs

• Can cause root damage and bark splitting and canker development

• Early fall frost/freeze and late spring frost/freeze are the most susceptible times for most plants

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http://www.forestryimages.org/images/768x512/5367177.jpg


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Weather: Spring Freeze Injury-Deciduous

• Blackened, wilted tissue

• Dead twigs, buds

• Sprouting

Freeze Injury

• Tip of leaf exposed

Spring Freeze Injury – Spruce, Fir

Iowa State University

Freeze – Rose Flowers• Spring/early summer 2008

• “Bullheading”

• Cold at time of floral organ development

Freeze- Summary

• Shows up 1-2 days after event

• Rapid necrosis

• Uniform damage to same-aged leaves

• Malformation to less severely damaged plant parts

• Late spring & early fall are most common times for low temp plant (flower/foliage) injury• Water freezes and disrupts cell membranes• Symptoms may resemble foliage/shoot diseases caused by

pathogens

Moisture

• Low soil moisture effects• Plants grow poorly• Plants are unproductive• Stunted appearance• Usually pale green to light

yellow• Can wilt and die• Scorched leaves• Dieback

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Moisture

• Scorch: Leaves turn brown from outer edges inward; generally evenly distributed around the leaf margin

Moisture

• Winter desiccation common on conifers• Needle scorching• Twig dieback

• Frozen soils don’t allow for water uptake which is needed because of transpiration during winter

Moisture

• Winter desiccation: needles brown from tips inward

Drought Injury Examples

How Does Drought Happen?

• Water lost faster than replacement

• May not have sufficient water for roots

• Water available, BUT roots not functioning/soil frozen

• Stem/trunk damage

Additional Facts:

• New growth usually masks damage

• Large percentagemust be damaged before plant health endangered

• Feel buds to check health

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Additional Facts:

• Disease organism erupts through needles

Hyg.ipm.illinois.edu

Cold damage starts at tips of needles and moves down; no organisms erupt through needles

Drought Management

• Identify possible causes/correct

• Fall and winter water: apply water monthly to absorbing roots from Nov 1 - March 1

• Fall water most critical

• Roots still functioning until soil temp drops below 40 degrees

[email protected]

Why Do Roots Not Function Well?

• Soil compaction

• Construction damage

• Dehydration

• Suffocation

• Planted too deep

•Leaves smaller than normal•Poor plant growth/yellowing•Slow death

Oxygen Starvation

Soil Oxygen Starvation

• Soil compaction

• Excess water

• Poor soil drainage

• Poor siting

• Excess mulch

• Stem girdling roots

Cultural/Soil Problems:Oxygen Starvation

• Leaves yellow/die from inside of plant outward and bottom up

• Premature leaf drop

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Stem Girdling Roots

• Holes too small, narrow

• Plant too large for container

• Soil texture differences

Symptoms of Stem Girdling Roots

• Off color foliage

• Smaller leaves

• Leaf scorch

• Dieback

• Early fall color

• Lower trunk bulged/flattened

Oxygen Starvation Caused by:

Compacted soil


• Impermeable/slowly impermeable soil coverings

Mulch Volcanoes

• Traps/retains moisture….or sheds it

• Suffocates phloem under bark

• Root growth into mulch instead of soil

• Rodents/other mammal feeding


Excess water

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Flooding• Standing water

• Sediment

• Even short term flooding can cause damage to trees• Moving soil from root

zone

• Oxygen deprivation


• Planting too deep• No root flare

Tree Planting Depth Cultural example:

Overwatering, poor soil drainage

Possible Tree Damage Symptoms From Oxygen Starvation

• Iron chlorosis

• Crown dieback

• “Early fall”

• Poor growth

Oxygen Starvation Management

Determine the cause/make corrections (sometimes corrections are not possible)

• Improve soil drainage/ aeration

• Remove black plastic

• Pull mulch away from base

• Reduce mulch thickness

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Wind Damage

Rubbing

Tattering

Nutrients

• Macronutrients• Needed in relative large

quantities by plants• N, P, K

• Micronutrients• Most soils contain

sufficient micronutrients for growth but there are exceptions

• Ca, S, Fe, Mg, Mn, B, Zn

Nutritional Deficiencies

• Nitrogen• Highly mobile in plants• Plants grow poorly• Light green in color• Lower leaves turn

yellow or light brown• Stems are short and

slender


• Calcium• Young leaves become

distorted with tips hooked back and margins curled

• Leaves may be irregular in shape and ragged with brown scorching or spotting

• Terminal buds finally die• Plants have poor, bare root

systems• Causes blossom end rot of

many fruits• Increases fruit decay in

storage

Blossom End Rot• Physiological disorder caused by Ca

deficiency• Ca important component of cell walls,

membranes

• Very fast growing tissues (like fruit) may not have enough Ca, causing problems with cell wall formation

• Certain plants and varieties more prone to damage

• Damage more severe early in growing season

• Avoid rapid plant growth• Excessive N fertilizer and soil moisture

fluctuations promote disorder

Blossom End Rot

• Apply water to garden plants more evenly

• Apply mulch to soil to keep moisture levels more even

• Avoid excessive nitrogen fertilization

• Calcium sprays don’t work; calcium must be transported through vascular tissue

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• Iron• Young leaves become

severely chlorotic• Main veins remain

characteristically green• Sometimes brown spots

develop• Part of or entire leaves

may dry• Leaves may be shed

Factors that Aggravate Iron Chlorosis• Susceptible plant species

• Cool soils and conditions that restrict air movement

• Poorly drained soils

• Compaction or use of plastic mulching

• Removal of topsoil exposing lime-enriched soil

• Planting close to house foundations

Soil Amendments for Iron Chlorosis

• Acidifying nitrogen fertilizers• Ammonium sulfate

• Elemental sulfur• 1 to 1 ½ lbs sulfur per 100

square feet to lower pH by one unit (maybe)

• Iron sulfate

• Combination of sulfur + iron sulfate

Chemical Injury

• Cautions regarding diagnosing chemical injury:• Unless the client is willing to have the plant tested for

chemical injury, there can never be a positive diagnosis• When talking with clients, the terminology is ‘damage

appears consistent with’…………• Testing for chemicals is $$$$$$• Testing labs?

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https://hgic.clemson.edu/factsheet/maple-diseases-insect-pests/

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Chemical Injury • Symptoms vary, depending on

product/chemical/application

• Loss of green leaf color, loss of interveinal leaf color, wilting

Often there is twisting, curling, distortion, spotting, browning, discoloration

Chemical Injury

Phenoxy (growth regulator) herbicide damage

Chemical Injury

Phenoxy type herbicide

Herbicide Symptoms• Phenoxy herbicides

Chemical Damage Example:

Dicamba applied under tree’s dripline.

Herbicide Symptoms

• Upward cupping of leaves

• Epinasty=bending, twistingof petioles and stems

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Epinasty on Tomato

Glyphosate

Herbicide Symptoms• “Feathering” or strap- like leaves

Chemical Injury

aka phytotoxicity—toxic effect on a plant by a compound/chemical

Plant Problems Which Mimic Herbicide Injury

Arthropod Injury to Plants

Plant Problems Which Mimic Herbicide Injury

• Poor drainage or other root zone problems

• Salt spray injury

• Virus diseases

• Environmental stresses

• Nutritional deficienciesMg deficiency in apple

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Abiotic Disorders Recap

Plant EnvironmentInteraction







• Ask questions


Causal Agents of Plant Disease

• Biotic = living causes such as microorganisms

• Abiotic = non-living causes such as the environment

Biotic Causes of Disease

• Living organisms that cause plant problems• Fungi• Bacteria • Virus• Phytoplasma• Nematodes• Parasitic Plants• Animals (not covered here)• Insects (a different

presentation)

Fungi and Bacteria Are Spread by:

• Wind

• Water (rain, irrigation)

• Soil

• Animals (including us)

• Equipment

• Plant Material

• Insects

Fungi and Bacteria Infect by:

• Entering the plant through natural openings• Stomates• Lenticils

• Entering through wounds

• Producing enzymes that break down cuticle

Lenticels

Sooty bark canker

Wound

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Fungi and Bacteria Cause:

• Leaf spots and curling

• Galls

• Soft rots

• Wilts

• Cankers

• Stem and root rots

Fungi Characteristics:

• Variety of sizes

• No chlorophyll

• Most harmless to plant health (saprophytes)

• Most reproduce by spores

Margins?•Marginal areas often exist between dead and healthy tissue in fungal infections

Distinct margins usually point to fungal problem and will often have a halo around the margin

But Beware of Exceptions…

Some fungal diseases have feathery margins!

Black spot rose

Apple scab

Fungal ID Tips

• Dry, fluffy (fuzzy)

• Distinct borders

• Damage is random

Powdery Mildew • Gray or white web-like covering

• Looks like flour or talcum powder spill

• Host specific

• Requires humidity but not free moisture

• Very common on plants in Colorado

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Plant Damage from P.M.

• Aesthetic damage – discoloration• Reddening?

• Distortion

• Premature leaf drop

• Chronic stress

Powdery Mildew Management

Plant

Organism Environment

Fungicides, sulfur

Water

Potassium or sodium bicarbonate

Neem or horticultural oil

Time

Use Caution! Cultural Management

• Site correctly (avoid dead air pockets)

• Space for good air circulation• Prune/thin appropriately for

plant• Avoid over fertilization• Avoid overwatering• Keep water out of plant • Water early in day• Remove infected material• Rake up fallen leaves …why?

Marssonina Leaf Spot

• Characteristics:• Spots are necrotic,

various sizes • May cause premature

leaf drop• May lead to chronic

stress

Marssonina Leaf Spot

• Infection occurs at budbreak

• Problem appears mid summer

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Marssonina Leaf Spot Management

Plant


No resistant cultivars

Fungicide: Daconil(protectant - at bud break)

Rake up leaves

Proper spacing, thinning, pruning

Keep water out of canopy

Time

To Compost or Not to Compost, That is the Question…

• Must be “hot” compost ( at least140 degrees, consistent throughout the pile)

• Disease organisms are everywhere

Group Activity Activity 5

This picture and samples from the books

Activity 5

Black spot of rose

Cytospora Canker• Colorado’s #1 canker-causer

• Cottonwood, aspen, willow, spruce

• Weak pathogen, successfully attacks stressed plants

• What is a canker?• Sunken, usually discolored area • Fungal cankers contain fruiting

structures • Conductive tissue under canker is

killed

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Fruiting Structures embedded in the bark

Orange spore tendrils protruding from opened fruiting structures of aspen, cottonwood, willow

Colorado Spruce with CytosporaCanker

Cytospora Canker Management

Plant



No effective fungicides

Prune out affected tissue

Grow healthy tree

Time

Group Activity—How to Key Out a Problem But first, two things…

• Reference book

• Using a hand lens

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Activity 3

This picture and sample

Bacteria Characteristics:

• Single-celled, microscopic

• Move by flagella

• Reproduce by dividing in two

Bacteria ID Tips

• Often slimy

• Greasy or water-soaked appearance

• Stinky

• Leaf spots often angular

Example: Fireblight

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Fireblight

• Characteristics:• “Shepherd’s crooking”• Blossom blight• Fruit shrivels

• Damage• Bacteria kills tissue• Reduces food production• Affects fruit production• Aesthetics

Cankers form

Bacterial ooze formsBacterial Streaming

Fireblight Hosts:

• Must be in Rosaceousfamily

• Can occur on ornamentals, not just on pome-fruit bearing plants• Ornamental pears

• Apples• Fruiting pears

• Does not form on Prunus(cherry, plum)

Fireblight:

• Conditions:• Moisture present • Temperatures 60 to 65

degrees • Blossoms present in some

cases

• Fireblight spreads:• Insects (including pollinators)• From an old infection• Through pruning tools

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Fireblight Management

Plant


Plant resistant varieties

Proper spacing, thinning

Keep water out of canopy

Pruning Fireblight Damaged Trees

• Prune 6-12 inches below visible infection (when dormant; if not dormant prune at least 18 inches below visible infection)

• Disinfect pruning tool between cuts

• Use 1:9 bleach solution OR

• Disinfectant sprays, rubbing alcohol

Group Activity—Bacteria

Activity 4This sample and book

Virus Characteristics

• Submicroscopic particles

•Nucleic acid and protein

•Disrupt cell metabolism

•Obligate parasite (can’t survive outside of host)

•Systemic

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Viruses

• One virus may infect one or dozens of different species of plants

• Each species of plant is usually attacked by many different kinds of viruses

• A plant may be infected by more than one kind of virus at the same time

• Viruses do not form reproductive structures, such as spores

Virus Dispersal and Infection

• Spread by someinsects, nematodes; in plant material and mechanically (tools)

• Insect spreads virus during feeding

How Do Viruses Move from Plant to Plant?

• Terminology: Vector/vectoring

• Viruses cannot move on their own• Non-motile

• Transmission• Mechanical

• Vegetative

• Insects and other arthropods (mites)

• Nematodes

• Dodder

• Seed

• Pollen

• Plasmodiophoromcyetes• Protists (fungal-like) that infect roots and

transmit viruses

Insect Transmission of Plant Viruses: The Jargon

• Vector = insect (or other means) of transmitting the virus from plant to plant

• Non-persistent (stylet-borne; e.g. aphids)

• Semi-persistent (foregut-borne)

• Persistent (Leafhoppers, Thrips)

Viruses Cause Symptoms:• Mottling

• Mosaic

• Crinkling

• Stunting

• Leaf spots

Tomato Spotted Wilt Virus

• Wide host range (500+)

• Directly affects plant health

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Tomato Spotted Wilt Virus• Transmitted by thrips

• Symptoms include stunting, fruit distortion, leaf flecking, dieback

TSWV Symptoms

• Wilting, spotting, crinkling

Ces.ca.uky.edu

TSWV Symptoms

Ringspots may form

Cankers may form

TSWV symptoms

Ringspots, malformation of fruit

Vector: Western Flower Thrips

•Larvae are tiny (1/16”), tubular•Pupate in soil under plant OR•In crevices on plant or in flowers

Recognizing Thrips Injury

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Tomato Spotted Wilt Virus Management

Plant


Some resistant varieties (of tomatoes)

Remove infested plants

SpinosadSticky traps?

Other Virus Examples

Rose Mosaic Virus

Peony Ringspot Virus

Plant-disease.ippc.orstate.edu

Mechanical Transmission

• Classic example is tobacco mosaic virus• Virus affects

tobacco, tomato and many other solanaceous hosts

Photo courtesy D. Shew, N.C State

Tomato (Tobacco) Mosaic

• Mechanically transmitted

• Leaf yellowing and mottling; rugosity

• Fruit distortion

• Resistant varieties

Phytoplasma Characteristics

•Cellular

•Lack cell walls

•Obligate parasites (can’t live outside of host )

Phytoplasma Dispersal and Infection

• Infected plant material

• Insect vectors• Mostly leafhoppers• Migrate north

www.insectimages.org

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Phytoplasmas

• Characteristics:

• Distortion

• Sterile flowers

• Yellowing or purpling of foliage

• “Witches broom” or “rat tail” appearance

• Hairy roots (carrots)

• Several phytoplasmas:• Ash Yellows

• Aster Yellows

Phytoplasma Management

Plant



No chemical controls

Remove infected plants

Repeated sprays/short intervals (for insect control)

Parasitic Plants

• May have roots, stems, leaves and flowers

• Reproduce by true seeds• Have little to no

chlorophyll• Spread via:

• Sticky seeds• Wind• Animals

• Damage plants by removing food from the host plant

Nematode Characteristics:

• Microscopic roundworms (but not true worms)

• Plant pathogenic nemas have spear-like stylets (mouthparts)

• Require free water

• Reproduce by eggs

Mouth

Stylet Nematodes• Spread by:

• Moving in water

• Infected plant material

• Soil

• Insect vectors

• Symptoms of nematode problems:• Stunting• Yellowing• Root knots• Poor growth

• Wilting• Death

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How Do You Sort It All Out?

Abiotic• Uniform

• No signs

• Numerous species (usually)

Biotic• Random• Signs present (maybe)• One species or related species

Abiotic? Biotic?

• Random vs. Uniform

Group ActivityActivity 6Abiotic vs. Biotic

Activity 7: answer questions

These samples







• Ask questions


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Plant Problem Diagnosis Steps

• How do symptoms progress?• Biotic disease –

symptoms progress and nearby plants become infected.

• Abiotic disease –generally a lack of symptom progression.

• Exception – nutritional symptoms progress slowly.







• Ask questions


Plant Problem Diagnostic Steps

• Review cultural practices:• Proper planting

technique(s)?• Fertilizer use? • Pesticide application?

Phytotoxicity?• Insecticides• Herbicides• Fungicides

• Irrigation frequency and amount?

• Handwatering vs irrigation system?

• Soil type/compaction?







• Ask questions



• Observe patterns:• Determine prevalence

of problem• Large area/All plants –

generally abiotic• Scattered, localized –

generally biotic• Check for distribution of

symptoms

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Examine Smaller Branches (Twigs)

Growth Increments

• Overall health clue• Sometimes easier to determine on conifers


• Know the normal appearance of the plant






• Ask questions

• Consult literature/control measures/final diagnosis• Use site:edu after search term when looking on the internet

Ask Questions

• Consider:• Many folks don’t offer

(know!) all the information• About 6 major symptoms for

hundreds of causes• Cause may be what

homeowner is doing/not

Ask More Questions! (More clues)

• Age of plant? • Exposure of plant?• When first noticed?• Has it happened before?• How has the plant been cared for?• Any other plants damaged?• What time of year is it?• Weather concerns?

Examine Smaller Branches

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Look at Leaves Look at Flowers

Ask for Photographs

Lower trunk

Upper trunk

Analyze information

• Research/read/references

• Is a lab test needed?

• Do you need more info?

• Analyze information

Analyze information

• Start with biotic

• Move to abiotic

• Consider primary vs. secondary (contributing) factors

Primary vs. Secondary Factor

• What is really causing the problem? (1)

• What is contributing to the problem? (2)

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Significance of Findings

• Is IT a problem or normal?

• Is IT affecting plant health (or will it)?

• Is IT affecting aesthetics?

• What does the client want?

• What can reasonably be done?

• Provide the client with all research based information-let them decide the course of action

“The first surefire rule of plant diagnostics is nothing is surefire” - Boggs, Draper, Chatfield, Ellis, Boehm, the OSU Extension

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Plant Disease and Diagnosis€¦ · 24/02/2020 · Nutritional Deficiencies •Nitrogen •Highly...

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Transcript of Plant Disease and Diagnosis€¦ · 24/02/2020 · Nutritional Deficiencies •Nitrogen •Highly...